It is known in the art to use optical methods to obtain surface characteristic information about a three-dimensional object by imaging segments of the surface for the purposes of compiling the image information to obtain a greater "picture" of the surface. Examples of surface characteristics which are desirably imaged for analysis purposes are the imaging of striations formed on the land and groove surfaces of a fired bullet for forensic analysis purposes, molded articles (from plastic, metal diecast or even medical tablets) to determine the origin of the molded article from the analysis of mold created markings on the object, and other objects (typically metal) whose detailed surface may exhibit signs of fatigue used in non-destructive testing analysis.
In imaging three-dimensional objects, the quality of the analysis is highly dependent on the quality of the images of the surface. In turn, the quality of the surface images are typically dependent on optical characteristics such as lighting, focus and the angle of the object surface with respect to the optical axis of the camera. For this reason, it is desirable to adjust the position of the object under optical observation such that its surface at the point of imaging is perpendicular to the optical axis of the camera. In the mentioned U.S. Pat. No. 5,379,106 granted Jan. 3, 1995 to Applicant, an apparatus for monitoring and adjusting the position of an object under optical observation is disclosed in which the object is mounted with sufficient degrees of freedom so as to be adjusted to place the surface being imaged substantially perpendicular with respect to the optical axis. In particular, the use of a pair of planar laser beams is disclosed which facilitate recognition of the angle of the surface being imaged with respect to the optical axis so that the parameters of focus, pitch and drift can be easily adjusted.
When objects being imaged are of an unknown, and in particular, of an irregular shape, the adjustment of the position of the object under optical observation as it is being imaged (a very large number of images may be taken of the surface with a certain amount of overlap to create a larger composite image) requires much time and effort to get the position right as the object is moved along some imaging path.